1. Field of the Invention
The present invention relates generally to medical devices, and more particularly, relates to transcutaneous electrical stimulation treatment of obstructive sleep apnea.
2. Description of the Prior Art
Sleep apnea is a medical condition which effects a large segment of the population. It exists in several forms. Perhaps the most dangerous, called central apnea, is associated with a lack of central drive to breath or with a disruption of the neural pathways from the brain to the diaphragm muscles. Research has been progressing for some time with one mode of treatment being electrical stimulation of the phrenetic nerve, thereby controlling function of the diaphragm. William W. L. Glenn describes the nature of this research in "Diaphragm Pacing: Present Status" in Pace, Volume 1, pages 357-370, July - September 1978.
A second form of sleep apnea, and of most concern to the present invention, is that which obstructs the upper air passageways. This condition has numerous deleterious results including disturbance of the patient and sleep partner and loss of effectiveness of the sleep process resulting in excessive patient fatigue. Long term effects include hypertension and cardiac problems.
The simplest forms of treatment for upper air passage obstructive sleep apnea involve mechanical constraints. U.S. Pat. No. 4,304,227 issued to Samelson describes such a device. Various surgical techniques are also employed including tracheostomy.
Perhaps the most common technique is through the use of systems which detect the obstructive condition and alert the patient to the problem in some fashion. Examples of this type of system include: U.S. Pat. No. 2,999,232 issued to Wilson; U.S. Pat. No. 3,032,029 issued to Cunningham; U.S. Pat. No. 3,480,010 issued to Crossley; U.S. Pat. No. 3,593,703 issued to Gunn et al.; U.S. Pat. No. 3,696,377 issued to Wall; U.S. Pat. No. 3,998,209 issued to Macvaugh; U.S. Pat. No. 4,220,142 issued to Rosen et al.; and U.S. Pat. No. 4,593,686 issued to Lloyd et al. These devices employ a variety of techniques, but each tends to be based upon detection of the condition and producing an alarm. Unfortunately, the alarm may rouse the patient to the extent that patient's sleep is disturbed, thereby exacerbating the very problem caused by the apnea episode.
Recently, research has been conducted which shows that the obstruction within the upper air passageway may be cleared with electrical stimulation. Two articles, herein incorporated by reference, describing this research may be found in American Review of Respiratory Disease Volume 140, 1989 at pages 1279 through 1289. The first article is "Effects of Electrical Stimulation of the Genioglossus on Upper Airway Resistance in Anesthetized Dogs", by Hiroshi Miki et al. The second article is "Effects of Submental Electrical Stimulation during Sleep on Upper Airway Patency in Patients with Obstructive Sleep Apnea", also by Hiroshi Miki et al.
U.S. Pat. No. 4,830,008 issued to Meer discusses an implantable system for treatment of obstructive sleep apnea using electrical stimulation. The implanted sensor(s) are used to sense inspiratory effort and stimulate the nerves of the upper airway in synchrony with the respiration cycle. Because upper airway stimulation may not be required for each inspiratory effort, Meer proposes an embodiment which also senses muscular activity in the upper airway to inhibit stimulation for certain respiratory cycles. However, it is not clear that the added complexity and morbidity of an implantable system are justified in the absence of evidence that stimulation only during the inspiratory effort is either necessary or sufficient.